The present invention relates to mirror arrays, generally, and more particularly to signal routers.
Signal routing is an essential component in network design. Signal routing involves directing signals from one location to another. Traditionally, signal routing has employed semiconductor switching devices. However, with the commercial drive for faster and more responsive networks offering greater bandwidth, semiconductor switching devices have been identified as a bottleneck. As a result of the switching speed limitations of semiconductor devices, industry is developing networks that rely on a greater number of electro-optical components, including optically based signal routing devices.
One class of electro-optical components proposed for signal routers is micro-electromechancial system (MEMS) based mirror arrays. For more information on MEMS based mirror arrays, their operation and fabrication, see Aksyuk et al., U.S. Pat. No. 5,912,094, Aksyuk et al., U.S. Pat. No. 5,994,159, and Aksyuk et al., U.S. Pat. No. 5,995,688, all of which are commonly assigned with the present invention and hereby incorporated by reference. Principally, one or more mirror in a MEMS based mirror array is operatively controlled by an electrostatic force initiated by an associated series of control signals. In response to a series of control signals, the one or more mirror of the array is tilted to a specific coordinate around a pair of axes. The tilting mechanism, and details of its operation with respect to a MEMS mirror array are found in U.S. patent application Ser. No. 09/415,178, filed on Oct. 8, 1999, commonly assigned with the present invention and hereby incorporated by reference.
Referring to FIG. 1, a top view of a MEMS based mirror array 10 for reflecting optical signals is illustrated. Array 10 is a two by two matrix of mirrors 15 formed on a common substrate 20. One or more mirrors 15 of array 10 tilts around a first and/or a second axis, 25 and 30, in response to the series of control signals. An incoming optical signal, therefore, may be reflected in a direction specified by the tilt of a respective mirror 15 of array 10 as determined by the received series control signals. The ability of the mirror 15 to direct the reflected incoming optical signal enables array 10 to be employed within an optical signal router.
Additional considerations are required to design an optical signal router employing a MEMS based mirror array. One or more mirror is tiltable within a steering range to route the optical signals. The degree to which the one or more mirror may tilt within its steering range corresponds with the voltages of the series of respective control signals. These control signals may reach as high as 150V to enable a mirror to tilt within its entire steering range. Further, the mirrors of the MEMS based mirror array are positioned in close proximity to one anotherxe2x80x94approximately 1 mm. Therefore, with the possibility of high potential voltages and the close spacing between mirrors, unwanted particles introduced during manufacturing or packaging of the MEMS based mirror arrays may facilitate arcing between conductive elements of adjacent mirrors.
As a result of these limitations, a demand exists for a MEMS based mirror array wherein each mirror requires a smaller range than its steering range to route optical signals. A need also exists for a MEMS based mirror array wherein each mirror requires controls signals lower than 150V for positioning each mirror to route optical signals.
An optical device is disclosed for directing optical signals between a plurality of first ports and a plurality of second ports. The optical device has at least one array of mirrors, such as, for example, a MEMS based mirror array. One or more mirrors in the array may be tilted around a first and/or a second axis in response to a series of control signal. The full extent of the tilt of the mirrors of the MEMS based mirror array is referred to herein as a steering range. By controlling the tilt of each mirror, an optical signal may be routed from one port of the first plurality to another port of the second plurality. For the purposes of the present invention, the optical signals are collimated Gaussian beams. In one embodiment, the optical signals having a wavelength of 1550 nm.
The optical device includes at least one curved reflective component. The curved reflective component enables one or more mirrors of the MEMS based mirror array to route an optical signal from any port of the plurality of first ports to any port of the plurality of second ports. The curvature of the reflective component may be at least one of spherical, parabolic or conic. An exemplary reflective component 80 is shown in FIG. 3. By designing reflective component 80 with a spherical concave curvature, the distance separating component 80 and a mirror array 75, may be extended by a displacement distance, Z, beyond the Rayleigh range, ZR, without scattering the optical signals. For the purposes of the present disclosure, a Rayleigh range, ZR, is the approximate distance from the narrowest point of a Gaussian optical beam, or waist, to where the diameter of the beam expands by the square root of two. In one embodiment, the Rayleigh range, ZR, is approximately 50 mm, the displacement distance, Z, is approximately 20.7 mm, and radius of curvature of reflective component 80 is approximately 141.5 mm.
The curvature of exemplary reflective component 80 enables the reflection of an optical signal back to an exemplary mirror on mirror array 75 from the extended distance created by displacement distance, Z. At the extended distance, the optical beam passes through its waist and begins to diverge. The reflection of the optical signal, as received by array 75, however is not scattered. The optical signal does not scatter because of the curvature of diverging optical signal matches the curvature of the reflective component 80. In extending the separation beyond the Rayleigh range without scattering the optical signal, each mirror in array 75 requires less than the steering range for routing an optical signal with reflective component 80. The range required in one embodiment of the present invention is approximately 7.5 degrees, in comparison with a planar reflective component 65 of FIG. 2(a) having a steering range of approximately 10.4 degrees.
These and other advantages and objects will become apparent to those skilled in the art from the following detailed description read in conjunction with the appended claims and the drawings attached hereto.